Pneumococcal disease is a leading cause of mortality and morbidity worldwide. The public health consequences have become ever more urgent due to the global emergence of drug resistant S. pneumoniae. This phenomenon appears to be due to the spread of a limited number of clones and serotypes and raises questions whether 1) S. pneumoniae clones emerge because they are drug-resistant and became predominant clones through antibiotic selective pressure;or 2) drug-resistant clones emerge because of their intrinsic virulence characteristics such as the pathogen's ability to induce persistent nasopharyngeal carriage or invade the host following colonization. These epidemiological questions have important implications for the potential use in developing countries of conjugate pneumococcal vaccines and programs to control the empiric use of antibiotics. However, no studies have addressed these questions in Latin America and other regions in the developing world. We propose a community-based study of invasive pneumococcal disease and nasopharyngeal colonization in Salvador, a city of 2.6 million inhabitants in Northeast Brazil. Since 1996, we have established at Fiocruz a continuous surveillance for pneumococcal meningitis and recently implemented the field site infrastructure to conduct longitudinal community-based studies. We therefore have an opportunity to obtain information on pneumococcal disease burden in Brazil and study its natural history. We propose a community-based study that aims to: 1) Measure the burden of invasive pneumocococcal disease in children from Salvador, Brazil and determine the clonal composition of S. pneumoniae strains that cause invasive disease. 2) Determine whether the ability of S. pneumoniae to produce nasopharyngeal carriage and invasive disease following colonization is influenced by the genotype, serotype or drug resistance status.